Ok guys. i am gonna have a custom grind made for a turbo setup (probably rear mount homemade). I know the general trend is either single pattern or a reverse split duration. My question is how much overlap is too little or too much. Is -3 degrees gonna make more power than a cam with -1 degrees overlap? I know the rule of thumb is -6 to 0 degrees is where you want to be. So ingeneral, what would be the hp/tq and powerband difference when comparing a cam with -3 degrees overlap compared to the same cam with -1 degrees overlap.

 

Nobody?

 

how much power you want to make

 

Generally, a well designed turbo will have around the same exhaust backpressure as boost. In the case, overlap will not hurt - it will only help power due to better scavenging. However, a rear-mounted turbo will inherently have more backpressure than even a poorly set-up front-mounted turbo, so less overlap is required to prevent exhaust from bleeding into the intake port. I would aim towards the -6 end of the scale.

 

Well, you are going to be paying for a custom cam, so the person doing the cam may be the best source of info. But as with all things cam, the best answer is "it depends". The location and size of the turbo and the amount of boost are major variables. Overlap is always a compromise. But in general I would look for "negative" overlap at 0.050" on a cam for a street turbo car. As far as race setups go, I am not familiar with them for turbos.

Rich

 

Sorry I didnt go into much detail. I originally was going to use a vortech, but decided on turbo. I have a Bret Bauer custom S/C cam and was thinking of selling it in favor a turbo cam. I will be running my forged 383 with AFR210's and a homemade rear mount setup. Exhaust will escape via Jet Hot LT's, mufflex y, and into a T70 turbo. Induction will consist of 3" tubing thru OBX front mount Air-Air up to monoblade (with alky spraying just in front) into a Stage 3 GTP ported LT4 intake. I plan on running 15psi. With that said, last night i used desktop dyno and setup a generic 383 with a agarret turbo from one of their pull down menus. I then swapped cams in and out to see how they affected the powerband. I also played with LSA's. Strangely enough, the more overlap the more hp/tq. Examples:

Bret Bauer S/C Cam (5 degrees overlap) - 729hp@5500/736tq@5000
XE230/236 .544 114 (5 degrees overlap) - 685hp@5500/702tq@5000
XE230/230 .598 114 (2 degrees overlap) - 710hp@5500/678tq@5500
XE230/230 .598 116 (-2 degrees overlap) - 707hp@5500/675tq@5500
XE230/224 .598/.560 (-1 degrees overlap) - 622hp@5500/626tq@4000

People always say that a small cam will make a ton of power with a turbo, but the difference in size between the SC cam I have and the 230/224 that I(was seriously thinking of going with) is big and there is a big difference in power/tq. Should I not even bother with desktop dyno, or is it a good way to see what specs of a cam will afftect the hp/tq and powerband?

 

I would NOT trust a desk top dyno for comparing cams. I've found them to be grossly inaccurate, especially in FI.

 

Mike, I am not worried about the hp/tq numbers. What I really wanted to see was how changing a cam affects the powerband. Whether it be changing LSA, duration, etc. Do you still think DD2000 isnt accurate in showing cam changes?

Bret Bauer told me that my SC cam would work fine with a turbo and its not worth the money to change to a turbo cam. DD2000 showed that his cam seemed to work great in both I dont know. What are some of the good softwares out there that is reliable? Thanks.

 

Engine Analyzer Pro is a lot more sophisticated than DD. But it's a lot more expensive and using it illustrates GIGO (Garbage In Garbage Out) in that it requires a variety of inputs that most of us don't have access to for reliable results. That said, DD has some utility. While I would never rely on it to predict the valid absolute numbers, I think it's useful to compare a small number of variables and get an idea of the trends that result. So, I think your use is valid and there may not be a lot of difference between the cams.

If Bret says it will work well, I'd believe it.

Rich

 

Cool. Thanks for the info. I'll check ou the EAP software, see if I can find it cheap. As you said, I was just changing cam variables and checking out how it affected power curve and such. I also used one of the turbos on DD, so it had surge cfm and, efficiency, airflow already programmed in. I guess I'll stick with it. I didnt doubt Bret, i just wanted to see if I should go with the mainstream (as far as trubo cams for a turbo'd car). Thanks guys.

Jon

 

How much power did you want to make?

I've tried a few cams in my car, and it has always gained peak HP, and more importantly held it for more RPM's with more overlap, even with the single turbo when backpressure was nearly double boost pressure.

When I switched from my 224/224 113lsa cam to my 218/218 114lsa cam, peak hp only dropped from 868rwhp to 847rwhp, but it dropped off much quicker, losing about 100rwhp @7000.

 

I would like to be in the 650-750rwhp range. My S/C cam is in the 23#/24# range for duration on a 116LSA.